1. Field of the Invention
The present invention relates to a drive device reducing the speed of rotational force output from a motor serving as a drive source, and transmitting the rotational force reduced in speed to a driven portion such as an upper slewing body, in a construction machine such as a shovel.
2. Background Art
The background art will be described by taking a rotation drive device for a shovel as an example.
The shovel includes a crawler type lower propelling body, and an upper slewing body installed on the lower propelling body so as to be slewable about an axis perpendicular to the ground. The upper slewing body is mounted with a working attachment.
The slewing drive device slewing the upper slewing body in this shovel is configured by a hydraulic motor or electric motor serving as a drive source, and a speed reduction unit including a gear mechanism reducing the speed of rotational force output from the motor and transmitting the rotational force reduced in speed to the upper slewing body as a driven portion.
The motor and the speed reduction unit are provided side by side in a state where a motor shaft as a central axis of the motor and a speed reduction output shaft as a central axis of the speed reduction unit are coaxial. Furthermore, the motor and the speed reduction unit are mounted on an upper frame in a state where the motor is located above the speed reduction unit.
The gear mechanism of the speed reduction unit is configured by a single-stage or multi-stage planetary gear mechanism including, for example, a sun gear, a planetary gear, and a ring gear. The output of the speed reduction unit is transmitted to the upper slewing body through a pinion provided on the speed reduction output shaft and a gear for slewing provided on a lower frame of the lower propelling body.
Furthermore, lubricant oil is injected into a casing of the speed reduction unit. The gear mechanism is lubricated with the lubricant oil. During operation of the slewing drive device, a part located near an outer circumference in the lubricant oil in the casing of the speed reduction unit rises along an inner wall surface of the casing due to a pumping action or centrifugal force occurring in connection with actuation of the gear mechanism. As a result, an oil surface of the lubricant oil in the casing becomes a mortar shape, or the lubricant oil in the casing is scattered upward. This phenomenon becomes more drastic when the oil surface of the lubricant oil rises with increase in the temperature of the lubricant oil. The part, which is located near the outer circumference in the lubricant oil in the casing and rises, immediately drops inward due to its own weight, and returns to a region where the gear mechanism is placed. The lubricant oil, which returns to the region where the gear mechanism is placed, increases resistance to agitation of the lubricant oil by the gear mechanism. As a result, there is caused a problem that an energy loss occurring at the time of the actuation of the gear mechanism increases.
Techniques shown in Japanese Patent Application Laid-Open Nos. 2008-232269 and 2008-232270 are publicly known as techniques solving this problem.
In these publicly known techniques, a tank is provided outside a casing, and an upper passage and a lower passage with a throttle are provided so as to straddle the outside and the inside of the casing. According to this configuration, lubricant oil rising such that an oil surface becomes a mortar shape is guided to the tank through the upper passage to be stored in the tank, and the lubricant oil stored in the tank is returned into the casing through the lower passage.
However, according to the aforementioned publicly known techniques, firstly, only the lubricant oil on a limited part in the lubricant oil moving upward such that the oil surface becomes the mortar shape over a whole circumference in the casing is guided to the tank through a narrow passage, and hence the lubricant oil does not reach the tank unless the whole lubricant oil is agitated with at least a certain level of agitating force. Consequently, the amount of the stored lubricant oil is reduced.
Secondly, in the aforementioned publicly known techniques, the upper passage and the lower passage join together on a connecting portion to the tank, and hence the lubricant oil stored in the tank may flow backward into the upper passage through the joining portion of the both passage due to its own weight. When the lubricant oil flows backward into the upper passage, the lubricant oil flowing backward becomes resistance to the flow of the lubricant oil moving toward the tank through the upper passage. As a result, the amount of the lubricant oil reaching the tank is increasingly reduced.
From these two points, in the aforementioned publicly known technique, an effect of reducing an energy loss caused by agitating the lubricant oil with the gear mechanism is low.
Furthermore, in the aforementioned publicly known technique, during operation of a slewing drive device, the lubricant oil flows in a substantial one-way manner from the casing to the tank, and the amount of the lubricant oil returning into the casing is extremely reduced. Consequently, at the time of continuous operation of the slewing drive device, and in a case where the operation and the shutdown of the slewing drive device are repeated, there is a possibility that the amount of the lubricant oil in the casing becomes reduced too much and lubrication insufficiency of a gear mechanism occurs.
Moreover, in the aforementioned publicly known techniques, since the tank, the upper passage and the lower passage are provided in the slewing drive device, the structure of the slewing drive device is complicated, and since the tank, the upper passage and the lower passage are provided outside the casing, the size of the slewing drive device increases. As a result, this may considerably increase the production cost of the slewing drive device and have a negative influence on a layout around the slewing drive device.
Moreover, in the aforementioned publicly known techniques, the size of the tank can not be increased from the stand point of suppression of increase in size of the slewing drive device, and consequently, the capacity of the tank can not be increased. Also from this aspect, the amount of the lubricant oil capable of being stored in the tank is reduced, and consequently the aforementioned energy loss reduction effect is further reduced.